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api/basic_json_document/node_count.md

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+# <small>nlohmann::basic_json_document::</small>node_count
+
+```cpp
+std::size_t node_count() const noexcept;
+```
+
+Returns the number of entries in the document's flat index.
+
+## Return value
+
+The number of index entries: one per value (of any type, at any nesting depth) plus one per object key. `0` for a
+[discarded](is_discarded.md) document.
+
+## Exception safety
+
+No-throw guarantee: this function never throws exceptions.
+
+## Complexity
+
+Constant.
+
+## Notes
+
+Each index entry is [16 bytes](../../home/architecture.md#node-index-of-json-views), so `#!cpp node_count() * 16` is
+the size of the index itself (part, but not all, of [`memory_usage()`](memory_usage.md), which also counts decoded
+strings and, for an owned document, the text).
+
+## Examples
+
+??? example
+
+    ```cpp
+    #include <iostream>
+    #include <nlohmann/json_view.hpp>
+    
+    using json_document = nlohmann::json_document;
+    
+    int main()
+    {
+        // node_count() is the size of the flat index: one 16-byte node per value,
+        // plus one per object key (values and keys are all the index stores)
+        json_document scalar = json_document::parse("42");
+        std::cout << scalar.node_count() << '\n';
+    
+        json_document doc = json_document::parse(R"({"a": 1, "b": [1, 2]})");
+        std::cout << doc.node_count() << '\n';
+    }
+    
+    ```
+
+    Output:
+
+    ```json
+    1
+    7
+    
+    ```
+
+## See also
+
+- [memory_usage](memory_usage.md) - the number of bytes held by the document
+- [shrink_to_fit](shrink_to_fit.md) - release unused index capacity
+
+## Version history
+
+- Added in version 3.13.0.